Form mats with grids of sharp pins are often used for forming acoustical surfaces in many applications, including aircraft engine covers such as cowls or nacelles. Pin areas or pinbeds are assembled from sections or sheets with grids of sharp pins, known as pinmats. The pins on these pinmats perforate the material being fabricated during lay-up and forming, forming an acoustically dampening surface. Surfaces formed with pinbeds often include fiber resin composites typically used for aircraft components. Pinbeds may be assembled by placing segments of pinmats on an underlying form or tool. The pinmats are cut to shape and adhered to the tool or form to produce a pinbed area on the form. Using several pinmats or trimmed pinmat sections, large and/or contoured areas on a form may be covered with pinmats. The material to be formed is then laid up on the form with the covering pinmats, or the form and the pinmats are pressed against the material being formed. After the form is removed from the product, the product is left with a perforated surface.
In other applications, contoured surfaces, ribbed surfaces, or smooth surfaces may be produced during lay-up and/or curing of formed products by utilizing textured mats attached to an underlying form or tool. As with pinmats, the textured mat is placed against the product being formed, leaving the desired surface after cure and removal of the form.
During assembly of pinbeds with pinmat segments, it is sometimes difficult to obtain tight contact between adjoining pinmats attached to the underlying form or tool. For example, a prior art pinbed 3 including four adjoining pinmats 5 with pins 7 is shown in FIG. 1. Between the pinmats 5 are gaps 10. The gaps 10 may also include corner mismatches, such as the corner mismatch 11, where adjoining corners of pinmats 5 meet. In this example prior art pinbed 3, there are approximately 100 pins square inch. The pins 7 are molded integrally with a backing mat. The pins 7 are approximately one-eighth inch high, and the mat is approximately one-eighth inch thick. The gaps 10 between the adjoining pinmats 5 may form a space where the material being formed can migrate during lay-up and cure, to a detriment of the final surface on the finished product.
More specifically, during forming and cure of heat activated fiber resin composites, such as utilized in aircraft, gaps 10 in the pinbed 3 can lead to resin lumps and lines in the final surface that need to be sanded down or otherwise corrected. Resin migration into the gap 10 can also occur, leaving a deficit of bonding resin or fiber movement in areas of the product adjoining the gaps. The gaps 10 can thus result in hand corrective work on the component being formed, and sometimes to the discard of the component. Resin may also penetrate gaps 10 and stick to the underlying forms (not shown), resulting in effort to clean the forms for subsequent use prior to subsequent forming operations. This may also cause undue wear or damage to the forms.
Gap filler materials have been utilized to fill gaps 10 in pinbeds 3 to decrease the difficulties resulting from gaps in the forming pinmats. The gap filler material contacts the part being formed prior to and during cure. Thus the material is preferably compatible with the underlying component material. Epoxy-based materials have been used as gap fillers, but can bond to the underlying tool. The use of epoxy materials for gap filling also includes curing time, and the epoxy can shrink, leaving part of the gap unfilled. Sheet adhesives compatible with fiber resin composites have been utilized to fill gaps. The film adhesive is cut into strips and rolled into “noodles.” The “noodles” are stuffed into gaps 10 by hand using a putty knife. With the installation of the film adhesive noodles done by hand, considerable time can be consumed filling forming gaps between the pinmats, especially in complex cured surfaces.
Therefore, a need exists for efficient application of a form gap filling material.